In order to successfully develop electrical and electronic devices based on high temperature superconductors in the Y.sub.1 Ba.sub.2 Cu.sub.3 O.sub.7 (Y123) family of materials, it is often necessary to fabricate thin crystallographically oriented films of the superconducting material. Oriented films of this type are particularly necessary for those applications that require the transport of high current densities in the superconducting state.
The preferred method of fabricating oriented thin films is by epitaxial crystallization on a suitable crystalline substrate. A suitable substrate material must have a small lattice constant mismatch relative to the thin film material and, additionally, it must not exhibit any significant degree of chemical reaction with the thin film components either during or after processing. It is difficult to find a substrate material that meets both criteria.
In the case of fabrication of thin films of the Y.sub.1 Ba.sub.2 Cu.sub.3 O.sub.7 family of materials, including those materials in which trivalent rare earths are substituted for the element yttrium, the substrates that have been previously employed include SrTiO.sub.3, MgO, cubic ZrO.sub.2, and Al.sub.2 O.sub.3. The best results were obtained with SrTiO.sub.3 ; however, Sr and Ti can migrate into and react with the superconductor film. Less satisfactory results were found for the other noted substrate materials. Although these materials are stable, they either exhibit unfavorable reactions at the interface or effects that lower the critical temperature of the superconductor. They are not conductive to controlled film orientation and they are relatively difficult to produce; therefore, there is a continuing need to provide a substrate material that has the desired properties.